Method and apparatus for lateral registration control in color printing

Abstract

A method and apparatus is provided for controlling the transverse registration of an image area to be exposed on a longitudinally moving belt by providing belt edge profile data, detecting a lateral position of the belt during movement of the belt by measuring the lateral position of the belt edge, and adjusting the transverse location of the image on the belt to compensate for a difference between the detected lateral belt edge position and the belt edge profile data. In addition, a method and apparatus is provided for controlling the lateral position of a longitudinally moving endless belt by generating a steering command signal by calculating a difference between the detected first lateral position of the belt edge and the belt edge profile data corresponding to the first longitudinal position, and adjusting the lateral position of the belt by steering the belt in response to the steering command.

Having thus described the invention, we now claim: 
     
       1. A method for transverse registration of an image area to be exposed on a longitudinally moving belt subject to lateral deviation from linear travel, said method comprising the steps of: providing belt edge profile data relating i) each of a plurality of longitudinal positions along said moving belt to ii) a lateral position of an edge of the belt with respect to a spatially fixed reference point;   detecting a first lateral position of said belt during movement of the belt by measuring the lateral position of said belt edge at a first one of said plurality of longitudinal positions along said belt; and,   adjusting the transverse location of the image area on the belt by shifting an active scan line to compensate for a difference between the detected first lateral position of said belt edge and the belt edge profile data related to said first one of said plurality of longitudinal positions.   
     
     
       2. The method for transverse registration of an image area according to claim 1 wherein: the step of providing said belt edge profile data includes the step of providing average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt repeatedly passing adjacent said spatially fixed reference point to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said spatially fixed reference point; and,   the step of adjusting the transverse location of the image area includes the step of adjusting the transverse location of the image area on the belt to compensate for a difference between the detected first lateral position of said belt edge and the average belt edge profile data related to said first one of said plurality of longitudinal positions.   
     
     
       3. The method for transverse registration of an image area according to claim 2 wherein: the step of providing said average belt edge profile data includes the step of providing moving average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt passing adjacent said spatially fixed reference point for a predetermined number of belt cycles to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said spatially fixed reference point for said predetermined number of belt cycles; and,   the step of adjusting the transverse location of the image area includes the step of adjusting the transverse location of the image area on the belt to compensate for a difference between the detected first lateral position of said belt edge and the moving average belt edge profile data related to said first one of said plurality of longitudinal positions.   
     
     
       4. The method for transverse registration of an image area according to claim 1 wherein the active scan line is shifted in a transverse direction. 
     
     
       5. The method for transverse registration of an image area according to claim 1 further including generating the active scan line from a transverse scan line which has a length greater than a length of the active scan line. 
     
     
       6. The method for transverse registration of an image area according to claim 5 wherein the length of the transverse scan line is greater than a length of the image area. 
     
     
       7. A method for transverse registration of an image area to be exposed on a longitudinally moving belt subject to lateral deviation from linear travel, said method comprising the steps of: providing belt edge profile data relating i) each of a plurality of longitudinal positions along said moving belt to ii) a lateral position of an edge of the belt with respect to a spatially fixed reference point;   detecting a first lateral position of said belt during movement of the belt by measuring the lateral position of said belt edge at a first one of said plurality of longitudinal positions along said belt;   adjusting the transverse location of the image area on the belt to compensate for a difference between the detected first lateral position of said belt edge and the belt edge profile data related to said first one of said plurality of longitudinal positions; and   determining when said longitudinally moving belt reaches a quasi steady state in said lateral deviation from linear travel by, calculating moving average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt passing adjacent said spatially fixed reference point for a predetermined number of belt cycles to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said reference point for said predetermined number of belt cycles,   detecting a first lateral position data set of said belt during movement of the belt by measuring the lateral position of said belt edge at said plurality of longitudinal positions along said belt,   calculating a plurality of difference data values by comparing said moving average belt edge profile data with said first lateral position data set for each of said plurality of longitudinal positions along said belt, and   realizing said quasi steady state when each of said plurality of difference data values are within a predetermined value range.     
     
     
       8. The method for transverse registration of an image area according to claim 7 wherein: the step of providing said belt edge profile data includes the step, after realizing said quasi steady state, of providing moving average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt passing adjacent said spatially fixed reference point for a predetermined number of belt cycles to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said reference point for said predetermined number of belt cycles; and,   the step of adjusting the transverse location of the image area includes the step, after realizing said quasi steady state, of adjusting the transverse location of the image area on the belt to compensate for a difference between the detected first lateral position of said belt edge and the moving average belt edge profile data related to said first one of said plurality of longitudinal positions.   
     
     
       9. The method for transverse registration of an image area according to claim 8 further comprising the steps, for each of said plurality of longitudinal positions along said belt, of: on-the-fly detecting a lateral position of said belt during movement of the belt by measuring the lateral position of said belt edge from said spatially fixed reference point; and,   on-the-fly adjusting the transverse location of the image area on the belt to compensate for a difference between the detected lateral position of said belt edge and the moving average belt edge profile data.   
     
     
       10. A method for controlling a lateral position of a longitudinally moving endless belt subject to lateral deviation from linear travel, said method comprising the steps of: providing belt edge profile data relating i) each of a plurality of longitudinal positions along said moving belt to ii) a lateral position of an edge of the belt with respect to a spatially fixed reference point;   detecting a first lateral position of said belt during movement of the belt by measuring the lateral position of said belt edge at a first one of said plurality of longitudinal positions along said belt;   generating a steering command signal by calculating a difference between the detected first lateral position of said belt edge and the belt edge profile data related to said first one of said plurality of longitudinal positions; and,   adjusting the lateral positions of the belt in response to said steering command signal while simultaneously performing the detecting and generating steps, whereby continuous updating of the lateral position of the belt is achieved.   
     
     
       11. The method for controlling a lateral position of a longitudinally moving endless belt according to claim 10 wherein: the step of providing said belt edge profile data includes the step of providing average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt repeatedly passing adjacent said spatially fixed reference point to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said reference point; and,   the step of generating said steering command signal includes the step of generating said steering command signal by calculating a difference between the detected first lateral position of said belt edge and the average belt edge profile data related to said first one of said plurality of longitudinal positions.   
     
     
       12. The method for controlling a lateral position of a longitudinally moving endless belt according to claim 11 wherein: the step of providing said average belt edge profile data includes the step of providing moving average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt passing adjacent said spatially fixed reference point for a predetermined number of belt cycles to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said reference point for said predetermined number of belt cycles; and,   the step of generating said steering command signal includes the step of generating said steering command signal by calculating a difference between the detected first lateral position of said belt edge and the moving average belt edge profile data related to said first one of said plurality of longitudinal positions.   
     
     
       13. A method for controlling a lateral position of a longitudinally moving endless belt subject to lateral deviation from linear travel, said method comprising the steps of: providing belt edge profile data relating i) each of a plurality of longitudinal positions along said moving belt to ii) a lateral position of an edge of the belt with respect to a spatially fixed reference point;   detecting a first lateral position of said belt during movement of the belt by measuring the lateral position of said belt edge at a first one of said plurality of longitudinal positions along said belt;   adjusting the transverse location of the image area on the belt to compensate for a difference between the detected first lateral position of said belt edge and the belt edge profile data related to said first one of said plurality of longitudinal positions; and   determining when said longitudinally moving belt reaches a quasi steady state in said lateral deviation from linear travel by, calculating moving average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt passing adjacent said spatially fixed reference point for a predetermined number of cycles to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said reference point for said predetermined number of belt cycles,   detecting a first lateral position data set of said belt during movement of said belt by measuring the lateral position of said belt edge at said plurality of longitudinal positions along said belt,   calculating a plurality of difference data values by comparing said moving average belt edge profile data with said first lateral position data set for each of said plurality of longitudinal positions along said belt, and   realizing said quasi steady state when each of said plurality of difference data values are within a predetermined value range.     
     
     
       14. The method for controlling a lateral position of a longitudinally moving endless belt according to claim 13 further comprising the step of determining when said longitudinally moving belt reaches a quasi steady state in said lateral deviation from linear travel by: calculating moving average belt profile data relating i) each of said plurality of longitudinal positions along said belt passing adjacent said spatially fixed reference point for a predetermined number of belt cycles;   detecting a first lateral position data set of said belt during movement of the belt by measuring the lateral position of said belt edge at said plurality of longitudinal positions along said belt;   calculating a plurality of difference data values by comparing said moving average belt edge profile data with said first lateral position data set for each of said plurality of longitudinal positions along said belt; and,   realizing said quasi steady state when each of said plurality of difference data values are within a predetermined value range.   
     
     
       15. The method for controlling a lateral position of a longitudinally moving endless belt according to claim 14 wherein: the step of providing said belt edge profile data includes the step, after realizing said quasi steady state, of providing moving average belt edge profile data relating i) each of said plurality of longitudinal positions along said belt passing adjacent said spatially fixed reference point for a predetermined number of belt cycles to ii) an average lateral position of said belt edge at each of said plurality of longitudinal positions along said belt with respect to said reference point for said predetermined number of belt cycles; and,   the step of generating said steering command signal includes the step, after realizing said quasi steady state, of generating said steering command signal by calculating a difference between the detected first lateral position of said belt edge and the moving average belt edge profile data related to said first one of said plurality of longitudinal positions.   
     
     
       16. The method for controlling a lateral position of a longitudinally moving endless belt according to claim 15 further comprising the steps, for each of said plurality of longitudinal positions along said belt, of: on-the-fly detecting a lateral position of said belt during movement of the belt by measuring the lateral position of said belt edge from said fixed reference point;   on-the-fly generating said steering command signal by calculating a difference between the detected lateral position of said belt edge and the moving average belt edge data; and,   on-the-fly adjusting the lateral position of the belt in response to said steering command.